Intra-ocular lens or contact lens exhibiting lardge depth of focus

ABSTRACT

Circular and annular lens zones are disclosed which, at a given lens area, exhibit a depth of focus of a lens of considerably smaller area. The large depth of focus is achieved by imparting the lens zones a refractive power profile. An assembly of such large depth of focus lens zones represents a lens of large diameter which lens, in polychromatic light, exhibits essentially the same depth of focus as the lens zones from which it is composed.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a lens and particularly to a lens whichexhibits a large depth of focus.

2. Description of the Prior Art

Lenses with two or more simultaneous foci or powers are known. Suchlenses, in particular in the form of contact or intra-ocular lenses, areused to correct presbyopia. The drawback of such lenses is that imagingis provided in distinct powers or foci, i.e. a “correct” image producedby the “correct” power is accompanied by a “wrong” image providedsimultaneously by a “wrong” power. As a consequence, the lens userfrequently experiences ghosting and halos with such lenses.

It is known that a lens of very small diameter exhibits a large depth offocus. This fact can be explained by wave optics considerations and iscalled the “stenopeic effect”. As an example, a “pinhole lens” of 1.3 mmdiameter exhibits a usable depth of focus of about 2.5 diopters. Thismeans that objects can be seen clearly even if they are out of focus by±1.25 diopters from the refractive focus of this pinhole lens. Such apinhole lens is therefore suitable to correct, or, more appropriately,“mask” presbyopia, since such a pinhole lens produces a clear image ofobjects the distance of which is between infinity (distance vision) andabout 40 cm (near vision) in front of this lens, or, if the lens is usedas a contact lens, in front of the eye.

It is further known, that such a pinhole lens also masks astigmatismwithin its available depth of focus. It is actually part of thediagnostic practice in the identification and quantification of theamount of astigmatism present in a human eye.

It should be noted that imaging with a pinhole lens of large depth offocus is absolutely free of ghosting, since imaging is not provided intwo or more distinct foci or powers. However, the drawback of suchpinhole lenses is reduced throughput of light intensity. As aconsequence, imaging of distant and near objects is not satisfactory indim light conditions.

This drawback can be eliminated with “zoned lenses” formed according tomy U.S. Pat. No. 5,982,543 (W. Fiala), the disclosure of which isincorporated by reference herein. It is shown there that an annular lensof small total area exhibits a large depth of focus as well. It isfurther shown there that an assembly of such annular lenses or annularlens zones provides the same depth of focus like the individual zones,if measures are taken such that the individual contributions of theindividual zones add incoherently. An analytical treatment of suchlenses can be found in: “W. Fiala et al: Numerical Calculation of aGiant Pinhole Lens in Polychromatic Light”; Annual Report 1996, page 39,editor: Physikalisches Institut, Universitaet Erlangen-Nuernberg”, thedisclosure of which is incorporated by reference herein.

In a lens according to U.S. Pat. No. 5,982,543 a rather large number ofannular zones is required in order to provide a sizeable depth of focus.In such a lens design, a depth of focus of at least one diopter requireslens zones the maximum area of which is limited to a value F=0.0056λmm², F being the maximum area of any of the lens zones, and λ theaverage wavelength in nanometers. Assuming the common value λ=550 nm,the maximum zone area is calculated to be 3.08 mm².

In order to achieve a depth of focus of 2.5 diopters with a lens madeaccording to my U.S. Pat. No. 5.892,543, the area of the individual lenszones exhibits a value of approximately 1.33 mm²; this means that a lensof 6 mm diameter would have to comprise twenty-one (21) such zones.Although the production of such a lens is possible, in principle, theproduction requirements are high

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lens of sizeablediameter which lens exhibits a large depth of focus and comprises fewerzones than a lens formed in accordance with my U.S. Pat. No. 5,982,543.

It is a further object of the present invention to provide a lens orannular lens of given area which exhibits a larger depth of focus than alens or annular lens of constant lens power and same area.

It is a further object of this invention to provide a lens with anincreased depth of focus, wherein the intensities of the powers withinthe depth of focus are approximately constant.

It is a further object of the present invention to provide a lens withincreased depth of focus, wherein the intensities of the powers withinthe depth of focus can be given desired values.

It is another object of the present invention to provide a lens withlarge depth of focus which lens is employed in the correction ofpresbyopia.

It is another object of the present invention to provide a lens withlarge depth of focus which lens is employed in the correction of cornealastigmatism.

It is yet another object of the present invention to provide a lens oflarge depth of focus which lens is employed in the correction ofirregular astigmatism.

It is still another object of the present invention to provide a lenswith large depth of focus which lens is employed in the correction ofregular or irregular astigmatism and which correction is independent ofthe angular position of the lens.

It is another object of the invention to provide a large diameter lenswith increased depth of focus which is easy to manufacture.

Other objects of this invention will become apparent in the course ofthe following discussion.

As will be shown in the following, the above-mentioned objects areachieved by imparting a lens or an annular lens a suitable refractivepower profile instead of a single refractive power. Such a lens or lenszone then exhibits a depth of focus which is substantially larger than alens or lens zone of single given power and of the same area. The powerprofile imparted to the lens or lens zone is available for designpurposes, i.e. different such power profiles result in differentintensity distributions within the depth of focus of the lens or annularlens. Using appropriate power profiles, it is therefore possible toattribute different relative intensities to different powers within theavailable depth of focus of the lens or annular lens. A lens of sizeablediameter and large depth of focus is provided by an assembly of suchlens zones, and measures are taken in order to achieve incoherentsummation of the contributions of the individual lens zones.

Specifically, the invention includes a lens zone exhibiting a depth offocus such that the lens zone includes a refractive power profile. Thepower profile is configured such that the depth of focus is at least 1.1diopters for light of 550 nm wavelength, and wherein the area of thelens zone is at least 3.14 mm². Preferably, the refractive power profileis more specifically configured such that the intensities within thedepth of focus are at least 50% (fifty percent) of the peak intensitywithin the depth of focus. Furthermore, the refractive power profile maybe configured such that the lens zone is a multifocal lens zone with atleast two powers such that at least one of the powers exhibits the depthof focus. It may also be considered that the power profile of the lenszone represents an approximation of a combination of at least oneconstant function and a fraction of a period of a sinusoidal function.

The present invention may include a lens exhibiting a large depth offocus which is formed from at least two lens zones. Each lens zone has arefractive power profile wherein the depth of focus is at least 1.1diopters for light of 550 mm wavelength and the area of each of saidlens zones is at least 3.14 mm². The lens is further configured suchthat optical path length differences are provided between adjacent lenszones such that light rays passing through adjacent lens zones have anoptical path length between an object point and an image point which aredifferent by at least a coherence length of the light used, which is atleast 1 μm. The lens of the present invention may include lens zonessuch that the refractive power profiles of the lens zones are identical.Alternatively, the refractive power profiles of the lens zones may beformed to be different. The lens may also be provided to be a multifocallens whereby each of the lens zones exhibits a refractive power profilehaving at least two powers and wherein at least one of the powersexhibits the depth of focus. The lens may be formed such that the areasof all lens zones are equal. Alternatively, the lens may be configuredsuch that the areas of all lens zones are different. The lens issuitable to be an ophthalmic lens, a contact lens, an intra-ocular lens,or an intra-corneal lens.

The lens of the present invention exhibits a large depth of focus byproviding at least two lens zones which include a central circular lenszone and at least one annular lens zone surrounding the circular lenszone. Each of the lens zones is configured such that light rays passingthrough adjacent lens zones have an optical path length differencebetween an object point and an image point which are different by atleast a coherence length of light passing through which is at least 1 μ.The area of any of the lens zones is at least 3.14 mm². The lens zonesare given refractive power profiles such that the depth of focus of anyof the lens zones is at least 1.1 diopters for light of 550 nmwavelength. The lens may be formed such that the shape of the throughfocus response of any of the lens zones is substantially identical withthe shape of the through focus response of the entire lens. The lens maybe used as an ophthalmic lens, a contact lens, an intra-ocular lens oran intra-corneal lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the through focus response (TFR) of a lens accordingto the present invention.

FIG. 2 illustrates the refractive power profile (“P1”) imparted to thecircular lens with TFR according to FIG. 1, wherein ΔD=D_(max)−D_(min)=3diopters.

FIG. 3 illustrates the TFR of another circular lens or annular lensaccording to the present invention such that higher effective lenspowers are weighted less than lower effective lens powers.

FIG. 4 illustrates a further refractive power profile (“P2”) imparted toa circular lens or annular lens with TFR according to FIG. 3, whereinΔD=D_(max)−D_(min)=3 diopters.

FIG. 5 (prior art) illustrates the TFR of a prior art lens of 1.2122 mmdiameter (area: 1.154 mm²) such that the depth of focus of this priorart lens is essentially equal with the depth of focus of the lensesaccording to FIG. 1 and FIG. 3.

FIG. 6 illustrates various TFRs of circular lenses (or annular lenseswith the same area as the circular lenses), wherein all circular lenses(or annular lenses) are imparted a power profile according to FIG. 2.

FIG. 7 illustrates the required diameter of a circular lens and therequired area of a lens zone as a function of the desired depth of focusfor a lens zone with constant refractive power and for a lens zone witha power profile P1 or P2.

FIG. 8 illustrates the TFR of a depth of focus lens of 4 mm diameterconsisting of four zones of equal area (Fresnel zones, area: 3.14 mm²each) in polychromafic light, wherein all zones exhibit the same powerprofile P1.

FIG. 9 illustrates another TFR of a depth of focus lens of 4 mm diameterconsisting of 4 zones of equal area (Fresnel zones, area 3.14 mm² each)in polychromatic light, wherein zones 1 and 3 exhibit power profile P1and zones 2 and 4 exhibit power profile P2.

FIG. 10 illustrates the cross-section of an embodiment of a depth offocus lens according to this invention.

FIG. 11 illustrates another refractive power profile imparted to lenszones according to this invention, wherein the refractive power profileis discontinuous and consists of four (4) discrete refractive powerswithin the lens zone.

FIG. 12 illustrates the TFR of a large depth of focus lens whichconsists of lens zones, each of which is imparted the power profileshown in FIG. 11.

FIG. 13A illustrates the TFR of yet another lens with large depth offocus, wherein the lens exhibits increased depth of focus in twodistinct powers and the lens zones exhibit a power profile as shown inFIG. 14.

FIG. 13B illustrates the TFR of lens having nine (9) Fresnel Zones on alens of 6.293 mm diameter, each zone having a power profile as shown inFIG. 14.

FIG. 14 illustrates the discontinuous power profile of the lens zones ofthe large depth of focus lens such that the TFR of which is shown inFIG. 13A and the TFR of the large depth of focus lens is shown in FIG.13B.

FIG. 15 illustrates various TFRs of yet another lens with large depth offocus according to this invention, wherein the TFRs are dependent onlens aperture or pupil size.

FIG. 16 illustrates various TFRs of a lens including lens zonesaccording to FIG. 15 but without steps between lens zones.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For the sake of simplicity and clarity, the following terms used in thisinvention disclosure are defined as follows:

“annular lens”: a lens which is confined to an annular ring with aninner bonding radius and an outer bonding radius.

“circular lens”: a lens which is confined to a circular disk of radiusr. (A circular lens is what is usually considered ‘a lens’).

“lens zone”: a lens zone is either a circular lens or an annular lens.The circular lens can be interpreted as an annular lens with innerbonding radius 0 and outer bonding radius r.

“Fresnel zones”, “Fresnel lens zones”: lens zones which exhibit the samearea π(r_(O) ²−r_(I) ²), r_(O) being the outer bonding radius and r_(I)being the inner bonding radius of one of the lens zones.

“refractive power profile”, “power profile”: the function D(x) of therefractive power at a radial distance x from the center of a lens zonevs. the squared distance x². The refractive power is calculated on thebasis of Snell's refraction law. Power profiles are called “P1, “P2”,etc.

“through focus response (TFR)”: the distribution of light intensityalong the axis of a lens or lens zone when a plane wave of light isincident on the lens or lens zone in parallel with the axis of the lensor lens zone.

“effective lens power”: the index behind a lens or lens zone divided bythe distance (in meters) on the lens axis behind said lens or lens zone.

“depth of focus”: the width in diopters of the TFR at a minimum of 40.5% of the peak intensity of the TFR, respectively.

“coherence length”: the value λ²/Δλ of a polychromatic light spectrum, λbeing the mean wavelength, and Δλ being the half-width of the wavelengthdistribution. The abbreviation “C.L.” is used in this disclosure. TheC.L. of white light is 1 micron (λ=550 nm, Δλ=300 nm).

The refractive power or power profile of a circular lens or annular lensdetermines the resultant wave front of light into which an incident,e.g. plane, wave is converted by this circular or annular lens. Thiswave front determines the resulting intensity distribution along theaxis of the circular lens or annular lens, i.e. it determines thethrough focus response (TFR). The calculation of the TFR as a result ofthe refractive power profile of a circular or annular lens zone can bedone analytically; one such method for this calculation is presented in:W. Fiala and J. Pingitzer: Analytical Approach to Diffractive MultifocalLenses, Eur. Phys. J. AP 9, 227-234 (2000), the disclosure of which isincorporated by reference herein. The algorithm presented in thispublication is used for the present calculations of the TFR of lensesand of assemblies of lens zones with optical steps between theindividual lens zones.

FIG. 1 illustrates the TFR of a circular lens of 2 mm diameterexhibiting a power profile P1 as shown in FIG. 2. For purposes of FIG.1, we assume a monochromatic light wavelength of 550 rum and apolychromatic mean wavelength of 550 nm and further a Gaussianwavelength distribution which results in a C.L of 3.1 microns. The TFRof FIG. 1 indicates that this lens zone exhibits a depth of focus inexcess of 3 diopters. Particular mention is made of the fact that thislens zone exhibits an area of 3.14 mm²; a lens zone with 3.14 mm² areaand constant refractive power would exhibit, by comparison, a depth offocus of only 1.1 diopters. It should also be noted that the intensitieswithin the depth of focus vary only slightly by comparison, which is anadvantage. In any case, the intensities within the depth of focus arelarger than 50% of the peak intensity. Also the fall-off of theintensities at the limits of the depth of focus is steep; the result ofthis steep fall-off is increased intensity within the usable depth offocus. Suitable refractive power profiles cannot easily be calculatedback from a desired shape of the TFR, since the resulting TFR isdetermined by diffraction effects rather than the refraction law(Snell's law). But with modem calculation tools it is possible to selectthe proper refractive power profile with a lens or annular lens zone fora desired shape of the TFR Such calculations are usually done on a“trial and error” basis.

FIG. 2 illustrates a power profile P1 of a lens zone of 3.14 mm² totalarea. The resulting TFR of such a lens zone is illustrated in FIG. 1.Power profiles and the resulting TFR of the above-discussed type of lenszone are suitable for correction of presbyopia and astigmatism. Inpresbyopia correction, it is occasionally desired to attribute morelight intensity to the distance power than to the near power, or viceversa FIG. 3 illustrates an example of such a desirous TFR. FIG. 3 showsthe TFR of a circular lens of 2 mm diameter (lens zone of 3.14 mm²)exhibiting a power profile P2 as shown in FIG. 4. Once again, we assumethe same parameters regarding the light wavelengths as set forth inFIG. 1. Such a lens or lens zone provides a sizeable depth of focus andintensity in the distance power and somewhat less intensity in the nearpower. Since the minimum intensity within the depth of focus is morethan 50% of the maximum intensity within the depth of focus, the fulldepth of focus is preserved within a range of over 3 diopters. As aconsequence, ghosting or halos will not be present with this lens zoneat all.

In FIG. 4, another suitable power profile P2 (i.e., the function D(x)versus x²) of a lens zone is illustrated which provides a non-symmetricintensity distribution in the TFR. The presented power profile providesmore intensity in the smaller powers of the TFR. The power profileaccording to FIG. 4 underlies the lens zones the TFR of which is shownin FIG. 3.

As said, the usable depths of focus of the discussed circular or annularlenses formed in accordance with FIGS. 14 was in excess of 3 diopters.The total lens area of these lens zones was 3.14 mm². For comparison, aprior art circular lens or annular lens of a given single refractivepower is shown in FIG. 5. Should such a circular or annular lens exhibitalso a depth of focus in excess of 3 diopters, the maximum area of thiscircular or annular lens has to be limited to 1.154 mm², i.e. a valuealmost a third smaller than the area of a circular or annular lensaccording to the present invention. A prior art lens zone of 3.14 mm²area would exhibit a depth of focus of only 1.1 diopters.

Should smaller values for the depth of focus be desired, the sameprincipal shape of a given power profile can be applied on lens zones oflarger area. The difference between the maximum and the minimumrefractive power in the power profile has to be adjusted accordingly.FIG. 6 illustrates three examples of TFRs of essentially similar shapebut having different depth of focus. The results are presented forcircular lenses of varying diameter. From the above discussion, it isevident that these results would also apply for annular lenses whichexhibit the same areas as the circular lenses. As can be seen from theresults in FIG. 6, the difference ΔD in the power profile as well as thediameter of the circular lens (or the area of an annular lens) determinethe available depth of focus. For example, a differenceΔD=D_(max)−D_(min)=2 diopters results in a lens or annular lens with adepth of focus somewhat in excess of 2 diopters; this depth of focuswill be in a lens of diameter 2.45 mm (area: 4.71 mm²). For other lensdiameters (or lens zone areas) the same difference ΔD would result inTFRs of different shapes. This is another example of the importance ofdiffraction phenomena associated with refractive lenses.

Thus, a circular lens or annular lens according to this invention canprovide a depth of focus which is much larger than that of a circularlens or annular lens of same area and given single power. The resultsare summarized in FIG. 7 and apply for lens zones which exhibit powerprofiles according to FIG. 2 and/or 4. As can be seen from FIG. 7, muchlarger lens diameters or lens zone areas are possible in a circular lensor annular lens according to the present invention than in aconventional circular or annular lens of same depth of focus. By way ofexample, a depth of focus of 2 diopters is achieved with a circular lensor annular lens of single refractive power of 1.77 mm² area, whereas acircular lens or annular lens according to the present inventionexhibits an area of approximately 4.9 mm².

An assembly of a central circular lens and surrounding annular lenszones according to the present invention represents a large aperturelens which exhibits the depth of focus of a much smaller lens. FIG. 8illustrates the TFR of a lens of 4 mm diameter; this lens consists offour lens zones of 3.14 mm² each; every lens zone exhibits a refractivepower profile like the one shown in FIG. 2, wherein D_(max)−D_(min)=3diopters. The innermost lens zone is a circular lens of 2 mm diameter.Every lens zone of the lens according to this invention exhibits a depthof focus of appr. 3.5 diopters; this large depth of focus is due to thefact that every lens zone is given a refractive power profile instead ofa constant refractive power. By comparison, lens zones of 3.14 mm² areaand constant refractive power would exhibit a depth of focus of only 1.1diopters.

It is also possible, to combine lens zones which exhibit different powerprofiles in a lens of large depth of focus and large diameter. FIG. 9illustrates an example for the TFR of such a lens according to thepresent invention. The lens of 4 mm diameter consists again of fourFresnel zones of equal area. Contrary to the example according to FIG.8, the individual lens zones do not exhibit the same refractive powerprofile. In the lens according to FIG. 9 the uneven lens zones exhibitthe refractive power profile according to FIG. 2 (P1) and the two evenlens zones feature the power profile according to FIG. 4 (P2). Bycombining lens zones of different power profiles it is possible tocreate a large aperture lens with large depth of focus wherein theintensity distribution within the depth of focus assumes a desiredfunction. The topographical dimensioning of the annular lens zones insuch a way that they exhibit a certain desired refractive power profileis state of the art and e.g. extensively discussed in WO 01/04667 A1 (W.Fiala), the disclosure of which is incorporated by reference herein.

The assemblage of annular zones such that the contributions of theindividual lens zones add incoherently, i.e. in independence of one theother, is state of the art and extensively discussed in U.S. Pat. No.5,982,543 (W. Fiala), the disclosure of which is incorporated byreference herein. Incoherent imaging is achieved by introducing opticalpath length differences between adjacent annular zones in excess of thecoherence length of the polychromatic light used in imaging with thislens. With these measures, the lens of large aperture exhibits the samedepth of focus in polychromatic light like the individual lens zones itis made up of.

By way of example, FIG. 10 shows part of a large depth of focus contactlens 1 according to the present invention; this lens consists of lenszones which exhibit refractive power profiles, and optical path lengthdifferences are provided between adjacent lens zones. In dimensioningthis lens, the position-of the focus pertaining to a given value D(x) ofthe power profile is calculated first; this position is given by thedistance n_(i)/(D(x) from the back vertex of the lens. From this focus,a light ray 5 is directed into the point P(z,x) on the envelope 6 of theback surface of the large depth of focus lens. This light ray is thenrefracted at the interface 6 between the immersion medium with index n,and the tear fluid 4 with index 1.336. Then the resulting ray isrefracted at the interface 3 between the tear fluid and the lens medium;the resulting light ray is then refracted at the interface 2 between thelens medium and the immersion medium. The resulting light ray after thisrefraction has to be parallel to the lens axis 7 (light incidence frominfinity): this can be achieved by variation of the inclination of thesurfaces 3 and 2 in a trial and error method. Surface 2, in general is amulti-curve; but it is also possible to design a lens with a front monocurve (e.g. a sphere).

The described procedure has to be carried out for all values of x of thepower profile D(x). Usually, the procedure starts with x=0 and then thevalue of x is increased in accordance with the given power profile. Whenthe value for x coincides with the outer bonding radius of theconsidered lens zone, a step 8 is introduced such that this stepprovides the required path length difference between adjacent lenszones. Step 8 is not necessarily in parallel with the lens axis 7. Thispath length difference is in the order of t(n₁−n_(tr)), wherein t is thetopographical step height, n₁ is the lens index and n_(tr) is the indexof the tear fluid. The topographical step height may have to be adjustedsuch that the optical path length difference assumes a certain desiredminimum value. Then the entire procedure as described above has to berepeated with new initial values for the (local) inclination of thefront surface 2.

As will be appreciated, the entire dimensioning procedure relies onmodern computation tools, since usually many trial runs are necessary inorder to arrive at the lens topography which corresponds to the requiredpower profile.

Should it be desired that the front surface is given by a mono curve(e.g. a sphere), then the steps 8 are a result of the chosen parameterswhich describe the front surface (e.g. front radius and centerthickness). Then a minimum optical step height T has to be defined, andthe relevant parameters have to be varied until all resultant steps 8are sufficiently large such that abs(t(n₁−n_(tr)))>T, where T is thedesired minimum optical path length difference. For the case of acontact lens, the index of the immersion medium is n_(i)=1. Bycomparison, the index of the immersion medium is n_(i)=1.336 for thecase of an intra-ocular lens; in the case of an intra-ocular lens, theindex n_(tr) of the medium adjacent to the lens will also assume thevalue 1.336. It may also be desired that the large depth of focus lensexhibits smooth outer surfaces, e.g. in the case of an intra-corneal orcontact lens. Then the “tear fluid” has to be a material with arefractive index n_(tr) which is either larger or smaller than the lensindex n_(i), i.e. n_(tr)>n₁ or n_(tr)<n₁. With these adjustments invalues for refractive indices, the described general dimensioningprocedure applies also for lenses other than contact lenses.

For a lens in air according to the present invention, both n_(i) andn_(tr) have to be given the value 1. The general dimensioning procedureagain applies also for lenses in air according to the present invention.

The steps can also be placed on the front surface of the lens. To oneknowledgeable in the art, it is obvious how the general dimensioningprocedure has to be adapted for the case where the steps are to bepositioned on the front surface of the lens.

In practice, power profiles like the ones shown in FIGS. 2 and 4,respectively, will be approximated discontinuously by a certain numberof discrete refractive powers. This approximation may be rather coarse,as demonstrated by the following example: FIG. 11 shows an approximationof power profile P1, and FIG. 12 shows the corresponding TFR of anassembly of lens zones which exhibit the power profile according to FIG.11. A comparison between FIGS. 1 and 12 indicates that the approximationof the power profile P1 (FIG. 2) by the values given in FIG. 11 isvalid. The TFR of FIG. 12 would apply for an intra-ocular lens withimaging properties both in distance (appr. 20 diopters) and near(approximately 24 diopters). This lens would also mask astigmatism dueto its large depth of focus.

Power profiles of lens zones can also be designed such that the lenszones are multifocal. FIG. 13B shows, as an example, the TFR of a largedepth of focus bifocal contact lens which comprises 9 lens zones on adiameter of 6.293 mm; all lens zones exhibit equal areas, i.e. the lensconsists of Fresnel lens zones. In this example, the area of all lenszones is 3.46 mm² as depicted in FIG. 13A. The shape of the TFR of anyof the lens zones (FIG. 1 3A) as well as the essentially identical shapeof the TFR of the entire lens (FIG. 13B) is due to the power profile ofthe lens zones according to FIG. 14. It is interesting to note that theintensity associated with the effective lens power of 4 diopters (FIG.13A and B) is very low, while half of the area of the lens zones exhibitthe refractive power of 4 diopters (FIG. 14). This is another example ofthe fact that due to diffraction effects the resulting distribution ofeffective powers of a lens zone, which is characterized by the TFR, isdifferent from the distribution of refractive powers (i.e., the powerprofile) given to this lens zone.

As is evident from the examples given in FIGS. 2, 4, 11 and 14, thepower profile given to the lens zones determines the depth of focus andthe shape of the TFR of the individual lens zone as well as the shape ofthe entire lens. Within these examples, the power profiles according toFIGS. 2 and 11 can be considered approximations of a combination ofconstant function, a half period of a sinusoidal function, and anotherconstant function. The power profile according to FIG. 14 would be acoarse approximation of three quarters of a period of a sine function,and the power profile according to FIG. 4 represents a combination of aninitial constant function and the approximation of a half period of asinusoidal function consequently, the disclosed examples of useful powerprofiles can be considered approximations of a combination of at leastone constant function and the fraction of a period of a sinusoidalfunction. Naturally, those skilled in the art will appreciate that thescope of useful power profiles is not restricted to this kind ofapproximations.

A circular lens or annular lens zone of 3.46 mm² area and singlerefractive power would exhibit a depth of focus of 1 diopter. Thepresent lens comprising 9 lens zones of 3.46 mm² each has a depth offocus of 1.6 diopters in the lower power of 3 diopters and a depth offocus of 1 diopter in the higher power of 5 diopters. Consequently, thetotal depth of focus—which is manifest in two distinct powers—is 2.6diopters, i.e. 2.6 times larger than the depth of focus of a lens zoneof 3.46 mm² area and single refractive power.

Lens zones exhibit the same TFR if their areas are equal (Fresnel zones)and if they exhibit the same power profile. Consequently, theperformance of a depth of focus lens which is composed of Fresnel zonesof identical power profile is practically independent of lens apertureor pupil size.

A lens according to this invention with a large depth of focus may alsobe composed of annular lens zones of unequal areas. Then the lensperformance will depend on lens aperture or pupil size.

FIG. 15 show various TFRs for a lens which is composed of lens zones ofincreasing area from center to rim. In this example the outer bondingradius r_(n) of the n-th lens zone is given byr _(n) =r ₁ ×n ^(0.6)and, consequently, the area an of the n-th zone assumes the valuea _(n) =a ₁ [n ^(2×0.6)−(n−1)^(2×0.6)]wherein r₁ and a₁ are the radius and the area of the first zone,respectively. (Fresnel zones would exhibit the exponent 0.5 instead of0.6 in the above equations.) The area al of the innermost lens zone is3.46 mm². All lens zones of the lens according to FIG. 15 are given therefractive power profile according to FIG. 14.

As can be seen from FIG. 15, the TFR of this depth of focus lens isdependent on lens aperture or pupil size, in contrast to the aboveexamples. The total depth of focus is distributed over two powers. Forall lens apertures the sum of the depths of focus in the two powers isat least twice as large as the depth of focus of a lens zone of constantrefractive power and 3.46 mm² area, which is the area of the smallestlens zone of the lens according to FIG. 15. As can be seen from FIG. 15,the minimum depth of focus in either the lower or the higher power ofthis lens is 1.2 diopters, which is 1.2 times the depth of focus of alens zone of constant power and 3.46 mm² area.

The introduction of optical path length differences is of paramountimportance for the desired lens performance. This is obvious from acomparison of the FIGS. 15 and 16: FIGS. 15 and 16, respectively, showthe TFRs of lenses which consist of the same lens zones, but opticalsteps of 5 microns are introduced in one lens (lens of FIG. 15), whereasthe transitions between adjacent lens zones are smooth in the other lens(lens of FIG. 16). Since in the lens according to FIG. 16 thecontributions of the various lens zones do not add incoherently,diffraction effects between zones result in rather undesirable TFRs ofthis lens.

As will be understood, numerous other possibilities exist for thecombination of lens zones with equal or unequal areas and equal orunequal refractive zone power profiles. FIG. 15 gives the results forjust one example.

In summary it has been shown that a large depth of focus can be given acircular lens or an annular lens, if this circular lens or annular lensis imparted an appropriate refractive power profile. As particularlyshown in FIG. 7, the depth of focus of a lens zone of given area couldbe almost tripled in comparison with a lens zone of same area andconstant refractive power by imparting the lens zone an appropriaterefractive power profile. It has been further shown that the depth offocus of a lens zone of constant refractive power can be achieved by alens zone of approximately 2.7 times larger area, if the larger arealens zone is imparted an appropriate power profile. Furthermore, it wasparticularly shown that the depth of focus of a lens which is composedof annular zones of areas in excess of 3.08 mm² exhibit a depth of focuswell in excess of 1 diopter, if the lens zones of this lens exhibitappropriate refractive power profiles instead of single refractivepowers. While prior art lenses according to U.S. Pat. No. 5,982,543require lens zones with a maximum area of 0.0056,λ mm², i.e. 3.08 mm²,for achieving a depth of focus of 1 diopter, the lens according to thepresent invention achieves this depth of focus of 1 diopter with lenszones of an area of almost 10 mm² (see FIG. 7).

Although the illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beeffected therein by one skilled in that art without departing from thescope of the invention.

1. A lens zone exhibiting a depth of focus comprising a refractive powerprofile configured such that said depth of focus is at least 1.1diopters for light of 550 nm wavelength, and wherein the area of saidlens zone is at least 3.14 mm².
 2. A lens zone according to claim 1,wherein the refractive power profile is configured such that theintensities within the depth of focus are at least 50% of the peakintensity within the depth of focus.
 3. A lens zone according to claim1, wherein the refractive power profile is configured such that the lenszone is a multifocal lens zone with at least two powers and wherein atleast one of the powers exhibits said depth of focus.
 4. A lens zoneaccording to claim 1, wherein said lens zone is an annular lens.
 5. Alens zone according to claim 1, wherein said lens zone is a circularlens.
 6. A lens zone according to claim 1, wherein the power profilecomprises an approximation of a combination of at least one constantfunction and a fraction of a period of a sinusoidal function.
 7. A lensexhibiting a large depth of focus comprising: at least two lens zoneseach lens zone having a refractive power profile wherein the depth offocus is at least 1.1 diopters for light of 550 nm wavelength andfurther wherein the area of each of said lens zones is at least 3.14mm², and wherein 5 optical path length differences are provided betweenadjacent lens zones such that light rays passing through adjacent lenszones have optical path lengths between an object point and an imagepoint which are different by at least a coherence length of light, whichis at least 1 μm.
 8. A lens according to claim 7, wherein the refractivepower profiles of the lens zones are identical.
 9. A lens according toclaim 7, wherein the refractive power profiles of the lens zones aredifferent.
 10. A lens according to claim 7, wherein the each of the lenszones exhibits refractive power profiles exhibiting at least two powersand wherein at least one of the powers exhibits said depth of focus. 11.A lens according to claim 7, wherein the areas of all of the lens zonesare equal.
 12. A lens according to claim 7, wherein the areas of all ofthe lens zones are different.
 13. A lens according to claim 7, whereinthe lens is an ophthalmic lens.
 14. A lens according to claim 7, whereinthe lens is a contact lens.
 15. A lens according to claim 7, wherein thelens is an intracular lens.
 16. A lens exhibiting a depth of focuscomprising: at least two lens zones including a central circular lenszone and at least one annular lens zone surrounding the central circularlens zone, all lens zones configured such that light rays passingthrough adjacent lens zones have an optical S path length between anobject point and an image point which are different by at least acoherence length of light, passing through which is at least 1 μm,wherein the area of any of said lens zones is at least 3.14 mm² andwherein the lens zones are given refractive power profiles such that thedepth of focus of any of the lens zones is at least 1.1 diopters forlight of 550 nm wavelength.
 17. A lens according to claim 16, whereinthe refractive power profiles of all lens zones are equal.
 18. A lensaccording to claim 16, wherein the refractive power profiles of each ofthe lens zones are different.
 19. A lens according to claim 16, whereinthe areas of all lens zones are equal.
 20. A lens according to claim 16,wherein the areas of each of the lens zones are different.
 21. A lensaccording to claim 16, wherein the shape of the through focus responseof any of the lens zones is substantially identical with the shape ofthe through focus response of the entire lens.
 22. A lens according toclaim 16, wherein the lens is an ophthalmic lens.
 23. A lens accordingto claim 16, wherein the lens is a contact lens.
 24. A lens according toclaim 16, wherein the lens is an intra-ocular lens.
 25. A lens accordingto claim 16, wherein the lens is a intra-corneal lens.